Intravenous immunoglobulin can induce antibody-dependent cell-mediated cytotoxicity and upregulate FCGR3A and FcγRIIIA expression in vitro

Background: Mechanism of action of intravenous immunoglobulin (IVIG) is complex, and involves the immunoglobulin G (IgG) Fc fragment binding to Fc receptors on immune cells as activators and inhibitors. Antibody-dependent cell-mediated cytotoxicity (ADCC) is a mechanism that mainly depends on FcγRIIIA. However, the IVIG Fc fragment-binding activity to FcγRIIIA is unknown, and the IVIG-mediated ADCC remains to be clarified. This study attempts to explore the IVIG-mediated ADCC and provide correlative evidence. Methods: This study evaluated the IVIG-mediated ADCC using a time-resolved fluorescence (TRF) cell cytotoxicity assay in vitro, and Jurkat-NFAT-Luc-CD16 cells were used to detect the IVIG Fc fragment-binding activity to FcγRIIIA. Quantitative real-time polymerase chain reaction (PCR) analyses were conducted to detect mRNA synthesis when IVIG incubated with effector cells, and the final expression of FcγRIIIA on the cell membranes were detected by flow cytometry. Results: The results showed that IVIG had optimal binding activity to FcγRIIIA fitted with a four-parameter curve equation regression model with R2=0.99 and caused specific ADCC of about 40%. Meanwhile, IVIG upregulated the expression of FCGR3A by two-fold, and the FcγRIIIA level was markedly increased from 33.7% up to 66.7%. Conclusions: This study investigated the IVIG-mediated ADCC, including measurement of the IVIG Fc fragment-binding activity to FcγRIIIA and the regulation of FcγRIIIA expression by IVIG. The results indicate that ADCC that can kill tumor cells and IVIG can also promote FCGR3A synthesis, increasing FcγRIIIA expression on immune cells membranes. The findings provide further evidence for the IVIG-mediated ADCC and understanding of the biological activity of IVIG.